Cutting tools, such as milling cutters, are rotatable tools of cylindrical, conical, shaped or disk form, having a plurality of cutting edges. Such cutters are available in many forms, such as plain cylindrical, side milling cutters, face and end mills, formed cutters, and standard and special shaped profile cutters.
End mills employing cutting inserts mounted at the front end of the tool are known in the art. The end mills can be used in several types of applications depending on the configuration of the cutting inserts mounted therein. The cutting inserts may present a peripheral cutting edge for side milling, a front cutting edge for face milling and a curved cutting edge of a so-called “ball-nose” end mill for various copying applications. Four flute mills are probably the most common, but 2, 3 or 6 flutes are also used extensively. End mills are in much used because they can execute a wide variety of milling operations, and the initial cost of the cutter is moderate. Shapes other than cylindrical are also in common use. The shank can be parallel or tapered, and need not necessarily be equal to the cutter teeth diameter.
Usually when an end mill is in operation, the machining force is exerted against one edge of the cutter. The resulting moment is resisted by the tool holder which rigidly grips the cutter shank. Ignoring the fact that the direction of the moment changes continually as the cutter revolves, the cutter can be considered to be stressed as a cantilever.
As shown in FIGS. 8-10, a conventional cutting tool 100, such as an end mill, includes a plurality of insert-receiving pockets 102 disposed between a plurality of flutes 104. Each pocket 102 includes a bottom support surface 106, a radial support surface 108 and an axial support surface 110 for supporting a cutting insert (not shown) when mounted in the pocket 102. Each pocket may also include a corner relief 112 at the intersection between the bottom support surface 106 and the axial support surface 110, and a threaded bore 114 for receiving a threaded fastener (not shown) for securing the cutting insert in the pocket 102. Simulations have shown that a tensile stress of the pocket 102 during machining operations of approximately 742 MPa is located proximate the axial support surface 110 and the corner relief 112, resulting in a safety factor of about 0.66.
While the matter of stress discussed above is related to avoiding fatigue that would result in tool breakage, no less important is the requirement to minimize tool deflection, in order to improve accuracy and surface finish and to reduce vibration and noise. The bending moment, along with the rotation of the cutter, produces a fully reversed stress condition (alternating tensile and compressive stresses), which is the most devastating condition for fatigue.
Accordingly, there is a need for an improved cutting tool that can overcome the limitations of the known cutting tool, and reduce or eliminate the overall stress of the cutting tool.